import java.util.LinkedList;
import java.util.Queue;

//岛屿数量
//测试链接： https://leetcode.cn/problems/number-of-islands/
public class NumIslands {
    int[] dx = { 0, 0, -1, 1 };
    int[] dy = { 1, -1, 0, 0 };
    boolean[][] vis = new boolean[301][301];
    int m, n;

    public int numIslands(char[][] grid) {
        m = grid.length;
        n = grid[0].length;
        int ret = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '1' && !vis[i][j]) {
                    ret++;
                    bfs(grid, i, j);
                }
            }
        }
        return ret;
    }

    public void bfs(char[][] grid, int i, int j) {
        Queue<int[]> q = new LinkedList<>();
        q.add(new int[] { i, j });
        vis[i][j] = true;
        while (!q.isEmpty()) {
            int[] t = q.poll();
            int a = t[0], b = t[1];
            for (int k = 0; k < 4; k++) {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' &&!vis[x][y]) {
                    q.add(new int[] { x, y });
                    vis[x][y] = true;
                }
            }
        }
    }
}
